sciencemag.org

Ask medieval historian Michael McCormick what year was the worst to be alive, and he's got an answer: "536." Not 1349, when the Black Death wiped out half of Europe. Not 1918, when the flu killed 50 million to 100 million people, mostly young adults. But 536.

Unlike a candidate today, the candidate in the ancient Mesoamerican city of Tlaxcallan would be starved, beaten with spiked whips when he fell asleep, and required to cut himself in bloodletting rituals before he could join the government.

No buts about it, the butthole is one of the finest innovations in the past 540 million years of animal evolution. Now, several unprecedented videos of gelatinous sea creatures called comb jellies, or ctenophores, threaten to upend the standard view of the evolution of the so-called through-gut.